docs: fix comment-rot, README Quick-Start scope, and benchmark inaccuracies

[endrju19]

Summary

Outcome of a repo-wide documentation audit (cross-checking every comment/KDoc against the code it describes). All changes are comment/KDoc, test-display-name, or markdown only — zero runtime behaviour change. Verified: ./gradlew ktlintCheck green, :okapi-core:test + :okapi-micrometer:test pass, all edited test sources compile.

Each fix was independently confirmed by an adversarial verifier that decided which side was correct — in every case here the code was right and the documentation was wrong (one separate genuine code bug found by the same audit is tracked separately, not in this PR).

Comment-rot / stale-reference / misleading

File	Was	Now
DeliveryInfo.kt	claimed CompositeMessageDeliverer routes by deserializing metadata	routes via OutboxEntry.deliveryType; serialize() is for the concrete deliverer's own deserialize
TransactionRunner.kt	non-existent modules okapi-spring / okapi-ktor	okapi-spring-boot / okapi-exposed
TransactionContextValidator.kt	"Standalone: no-op (always returns true)" — no such impl ships	"Standalone: user-provided implementation"
ExposedConnectionProvider.kt	TransactionManager.current()	currentOrNull() (matches code)
ConnectionLeakProofTest.kt	false history: "old getConnection(): Connection contract" that never existed	describes the design pitfall the test guards against
MultiDataSourceTransactionTest.kt	"PROPAGATION_REQUIRED nests via savepoints" (wrong)	REQUIRED joins the existing tx; savepoints are PROPAGATION_NESTED
MicrometerOutboxMetricsTest.kt	name/KDoc claimed "eager NaN before first refresh", contradicting its own inline note	retitled to match what it asserts (lazy refresh, no store query on construction)
OkapiLiquibaseAutoConfiguration.kt	@AutoConfigureAfter (×2)	@AutoConfiguration(after = ...)
OkapiMetricsProperties.kt	"Each refresh runs one transaction" (unconditional)	wrapped in a transaction only when a tx manager is available
OutboxAutoConfiguration.kt	"Requires a TransactionRunner bean" (unconditional)	required only when a scheduler is enabled (publish-only needs none)
LiquibaseAutoConfigurationTest.kt	brittle build.gradle.kts:35-36 ref (pointed at unrelated block)	dropped the line numbers
OutboxAutoConfigurationTransactionRunnerTest.kt	test name "...but currently is silent" (stale; assertion requires the WARN)	describes the asserted WARN-branch behaviour
ObservabilityEndToEndTest.kt	comment that just narrated the next two lines	removed

README — Quick Start scope

The Quick Start had drifted into reference-manual depth. Trimmed the FOR UPDATE SKIP LOCKED mechanism explanation to a one-liner + pointer, and moved (verbatim, nothing deleted) the mechanism paragraph, the multi-DataSource paragraph, the TransactionTemplate-precedence paragraph, and the direct-scheduler-construction block into a new Advanced: transactions & multi-DataSource section placed right before How It Works.

benchmarks/README

• Heap -Xms2g -Xmx2g → -Xms8g -Xmx8g (matches build.gradle.kts; 2g OOMs in throughput mode).
• Replaced the wrong "2 transports × 3 batchSize × 8 iterations" wall-time formula (HTTP actually runs 9 param combos via httpLatencyMs; warmup/measurement/fork were conflated) with an accurate matrix description.
• Fixed an untranslated word.

Test plan

• ./gradlew ktlintCheck — green
• ./gradlew :okapi-core:test :okapi-micrometer:test — pass
• :okapi-spring-boot:compileTestKotlin + :okapi-integration-tests:compileTestKotlin — compile clean (container E2E tests need Docker, unaffected — comment-only edits)
• Confirmed via diff: no runtime code changed (only comments, KDoc, two test display names, markdown)